Our family really enjoys the flexibility that the Park-Hopper options provides. We'd be very lost without it!
For example, we mistakienly believed all the posts regarding DAK being a 'half day' park... and assumed we could do it all in one day. WRONG! (My partner and I are both biologists, so we have a special added interest in DAK.) We didn't get through anywhere near the entrie park in one day, and had missed the Lion King show to boot. With PH, we were able to go back on another morning and visit the remaining attractions, without being committed to spending an entire second day at DAK. Also, on a lot of the evenings that other parks close earlier... we seem to find our way back to Epcot (DH's favorite, esp. during F&W Festival). Having PH meant that we could go into MGM one evening for dinner and then Fantasmic, without having had to spend the entire day at that park (MGM is our personal least favorite of the WDW parks--the thought of staying there from EMH opening through closing time just doesn't appeal to us). And we really like to keep our final day at WDW 'open', so that we can go back and visit everyone's favorite attractions one last time (without worrying about whether or not they are in different parks).
Everything at WDW is located in such close proximity, that it is very easy to park hop. And we tend to find it very relaxing to know that we can go anywhere in the 'World' that we want to, without being restricted to having to choose one specific park (and then being tied down to visiting only that park to the exclusion of anything else we might want to do that day).
It's all a personal preference, and some people really don't need the PH option (which is why it is an option... grin). But it sure was nice on our last visit, to be able to sit back and relax and take our time exploring the parks, while we watched other families frantically rushing from attraction to attraction (because it was their 'one day' for that specific park, and they wanted to be sure to see everything possible).